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It has earlier been reported that the human monoclonal antibody (MoAb 33G2) and polyclonal antibodies reactive with Pf332 may interfere in vitro with the erythrocytic cycle of Plasmodium falciparum at two potential target sites for protective antibodies, indicating that the antigen may constitute an important target for immune responses during malaria infections. MoAb 33G2 shows its highest reactivity with repeated sequences in the antigen Pr332 and also cross-reacts with determinants in Pf155/RESA. This study was conducted in order to assess the prevalence of seroreactivity against Pf332 in individuals residing in areas of different malaria endemicity, and in children with different degrees of disease severity. We now report that individuals resident in malaria endemic regions show a high prevalence of seroreactivity to antigen Pf332 repeat sequences. The mean antibody concentrations were significantly higher in donors from Liberia. Madagascar and Gambia compared with Thai and Colombian donors, probably reflecting the higher degree of exposure in the African regions. Although the levels of such antibodies in individual sera correlated well with the levels of antibodies to one Pf155/RESA repeat peptide, only a minor part of the peptidereactive antibodies were cross-reactive between the two antigens. In Gambian children, the mean concentrations of antibodies reactive with PD32 or Pf 155/RESA peptides were significantly higher in children with severe than with mild malaria. Further longitudinal studies are needed to evaluate the capacity of Pf332 to induce potentially protective or harmful antibody responses. [ABSTRACT FROM AUTHOR]

Antigenic diversity in held populations of Plasmodium falciparum parasites may delay the acquisition of protective immunity to malaria, the development of which may thus require repeated exposure to infection over a prolonged period of time. In this study we show that P. falciparum parasites may vary in their sensitivity to antibody-mediated invasion/growth inhibition in vitro. Wild isolates of P. falciparum from children living in an endemic area of Burkina Faso were tested for their sensitivity to the growth inhibitory effects of antibodies originating from the same (autologous) and front other donors (heterologous). A significantly lower invasion inhibition activity was obtained when the isolates and antibodies were tested in autologous compared with heterologous combinations. The lower sensitivity to growth inhibition by autologous antibodies may be due to immune pressure in vivo, selecting from a heterogeneous parasite population those with a low expression of the antigens recognized by the host's antibodies. Alternatively, the parasites cultured from each child might represent expanding parasite populations. mainly constituting strains not earlier seen by the immune system of that specific host. The results reinforce the concern about Plasmodium antigenic diversity as a major obstacle towards the development of an effective malaria vaccine. [ABSTRACT FROM AUTHOR]

T cells from patients with acute Plasmodium falciparum malaria were investigated for induction of immunoglobulin- or anti-malaria antibody secretion in vitro. Stimulation of autologous T/B cell mixtures (2T: IB) with low concentrations of P. falciparum antigen and cultured for 12 days gave rise to a T-dependent IgG secretion which was significantly elevated over that in medium controls. This was achieved with both a crude P. falciparum antigen and a partially purified preparation enriched in Pf 155. a merozoite-derived antigen deposited in the red cell membrane at invasion (Perlmann et al. 1984), Control antigen (RBC ghosts) induced IgG secretion only when added at high concentrations (>10 μg/ml). Neither of the antigens induced IgG secretion at concentrations of ≪ 10μg/ ml in control cultures of lymphocytes from patients with P. vita.\ malaria. Supernatants from cultures of P.falciparum patients frequently contained anti-P. falciparum antibodies when nanogram quantities (10-100 ng/ml) of either one of the two malaria antigen preparations was used for stimulation. No anti-P. falciparum antibodies were induced by the control antigen at any concentration. The induced anti-P. falciparum antibodies were directed to intracellular parasites and, at lower frequencies. to Pf 155 as detected on the surface of infected erythrocytes. The induction in vitro of anti-P. falciparum antibodies appeared to be correlated with the presence of such antibodies in the sera of the lymphocyte donors. The lymphocytes of only one out of eight P. vivax patients responded to antigen stimulation by secreting anti-P. falciparum antibodies. However, this donor (but not any of the others), was also P. falciparum seropositive. Taken together, these results indicate that the induction of anti-P. falciparum antibody secretion reflects a secondary response in vitro of cells primed in vivo. The present experimental system should be well suited to map parasite antigen for their capacity lo induce T cell dependent responses in P.falciparum malaria. [ABSTRACT FROM AUTHOR]

The mitogen-induced DNA synthesis in vitro in lymphocytes from 20 patients acutely ill with Plasmodium falciparum malaria was compared with that of 16 healthy donors. Within both groups part of the donors were individuals who had only experienced short exposure or none at all to the parasite (Sweden) while the other part were donors living in a malaria endemic area (Colombia), The proliferative response to the T cell mitogen La (leucoagglutinin from PHA) of the patients was significantly reduced as compared with that of the controls. With pokeweed mitogen which stimulates T cells and induces a T cell-dependent activation of B cells, no difference between patients or controls was seen. The results were similar for the donors of different geographical origin and malaria background. Lymphocytes and monocytes from the peripheral blood of these donors were also studied for surface marker distribution by means of monoclonal antibodies. Both the absolute and the relative frequencies of T cells in the blood of the malaria patients were significantly reduced as compared with the controls. Furthermore, in almost all eight patients tested, the ratio between T4+ T cells (including the helper/inducer subsets) and T8+ T cells (including the suppressor and cytotoxic subsets) were below 1: 1 while they were close to 2:1 in the controls. The results indicate that the relative frequency of T8+ T cells, expressed as percentage total T cells (T.3+ ) was significantly elevated in the P. falciparum patients. The possible relationship between this imbalance and the irregular La response of the patients lymphocytes requires further investigation of lymphocyte function. [ABSTRACT FROM AUTHOR]